To install and connect an integrated circuit chip on a main board which has electrical connection pads on a first face and which has electrical connection tracks linked to these pads and to electronic components mounted on this main board, it is known to provide an intermediate electrical connection board parallel to the main board.
This intermediate board has first electrical connection pads made on a first face for the connection of the chip, second electrical connection pads made on a second face, and electrical links between the first and second pads.
Electrical connection balls are placed in a space separating the intermediate board and the main board and are interposed between the second pads of the intermediate board and the pads of the main board.
According to a common embodiment, there is provided, in the space, a peripheral zone which comprises a peripheral matrix of five rows of balls, a central zone which comprises a central matrix of balls, and a middle zone devoid of balls which separates the peripheral zone and the central zone.
The main board also has tracks radiating outward which are linked to the balls of the outer row of the peripheral matrix and radiating tracks which pass between the balls of the outer row and are linked to the balls of the second outer row that is adjacent to this outer row.
The main board also has, in the middle zone, a matrix of two outer rows of electrical connection vias adjacent to the peripheral matrix, and has, on its aforesaid first face, short tracks radiating inward which link the balls of the two inner rows of the peripheral matrix and the vias, passing alternately between the balls of the inner row of balls and the outer row of vias.
The main board also has, in the middle zone, a matrix of two inner rows of electrical connection vias adjacent to the peripheral matrix, and has, on its aforesaid first face, short tracks radiating outward which link the balls of the two outer rows of the central matrix and the vias, passing alternately between the balls of the outer row of balls of this matrix and the inner row of vias.
The main board furthermore has, in the peripheral zone, electrical connection vias and short electrical connection tracks which link these vias to the balls of the middle row of the peripheral matrix.
This layout of vias in the peripheral zone in which the connection pads of the peripheral matrix are provided raises difficulties when seeking to reduce the pitch separating them.